Process of increasing the strength of insolubilized artificial protein filamets



Patented May 2, 1950 PROCESS 0F INCREASING THE STRENGTH OF INSOLUBIL'IZED ARTIFICIAL PROTEIN EFI'LAMENTS Robin H. K. Thomson, Kilvirinning, and Dav-id Traill, Ardrossan, Scotland, assignors to Imperial Chemical Industries Limited, a corporation of Great Britain No Drawing. Application J uly 26, 1945, Serial No. 607,272. In Great Britain "September 6, 1944 The present invention relates to the production of improved artificial insolubilised protein filaments of the kind wherein the .insolubilisation of the coag-ulated filaments obtained by wet spinning is carried out by means of formaldehyde in the presence of a strongly acidifiedsaline -.soluti0n.

' The invention is especially applicable to insolubil-ised filaments produced from alkalinesolutions of casein and alkaline solutions of vegetable glob- ;ulins, for instance, peanut globulin solutions or soya bean globulin solutions in dilute sodium hydroxide solution. The invention has for an object to increase the strength of the insolubilised protein filaments.

The insolubilisation of the coagulated wet spun protein filaments by means of formaldehyde can most effectively be carried out in a strongly acid :saline medium having a pH not exceedinglll, and preferably not exceeding 0.5. When the formaldehyde and the acid are employed in the same solution, as is usually most convenient, the formaldehyde content need not be more than a few per cent and is customarily much less than per cent, but at higher pHs the insolubilising effect of the formaldehyde is markedly decreased. The presence of the salt is required in order to prevent the swelling up and consequent loss of the filamentary form of the protein in the highly acid solution before it has had time to become insolubilised.

While it is known that stretching of the coagulated Wet spun filaments previous to their insolubilisation has a beneficial effect on the strength of the insolubilised filaments obtained from these, and that the strength of the insolubilised filaments can frequently be further increased by treatments involving further stretching, it is often inconvenient to stretch the filaments after they have been insolubilised and the effects produced are only temporary.

We have now found that a further improvement in the strength of the filaments obtained from coagulated protein filaments that have been insolubilised with formaldehyde in presence of strongly acidified saline solution as aforesaid and if desired washed to free it from 's'alts and uncom bined acid or formaldehyde, is obtained if the insolubilised filaments are treated with a strong aqueous formaldehyde solution having a pH between 1.9 and 4.0, preferably between 2.0 and 3.5.

According to the present invention, therefore, the method for the production :of improved artiflcial insolubilised protein filaments of the kind herein defined comprises treating the insolubilised filaments with a strong aqueous formaldel Claims. (Cl. 851-2716) hyde solution having a pH between approximately 1.9 and 450, preferably between '2;0 and 3.5.

The efiicacy of the formaldehyde in strength-.- ening the filaments is 'veryseriously diminished at a pH range only slightly below 1.9, and is also diminished, although somewhat less sharply,;in the acidic pH range above pH 4.

- The time for which the treatment will be carried on will depend on a number of factors in--- eluding the temperature and the formaldehyde concentration, but with formalin of commercial strength at room temperature brought to a ,pH

of 2.0 to 3.5 excellentv results are obtained if the treatment is carried on for half an hour to three quarters of an hour, and there is no advantage in prolonging the treatment unduly.

.Depending on the acidity at which the treat:

.ment is carried out, there maybe used. strong acids, bufieredfstrong acids, or weak acids of sufficiently high dissociation constant. Commercial formalin itself has usually an acid reaction and its acidity is often sufiicient for the purposes of the invention.

The invention is illustrated in the following example:

Example A matured alkaline solution of peanut globulin is spun into a coagulating bath consisting of an aqueous solution containing 1.5 per cent sulphuric acid and 20 per cent sodium sulphate at 30 C. from which it is withdrawn at a linear rate exceeding the linear rate of its extrusion and the coagulated filaments are stretched in a bath of the same composition. They are then wound on to a swift and immersed in a saturated sodium chloride solution at 30 C. for 10 minutes, after which they are out into staple fibre form. The staple fibre is then immersed in twenty times its dry weight of an insolubilising bath consisting of a solution containing 2.5 per cent sulphuric acid, 1.5 per cent formaldehyde and 26 per cent sodium chloride for 20 hours at 40 C. The resulting insolubilised staple fibre is then thoroughly washed with water and dried at 100 C. The filaments in the resulting staple fibre have an average strength of 7.7 kilograms per square millimetre as measured on the Cliff Autographic Recorder. They are practically unaffected in handle by treatment for minutes at 97 C. in a bath containing 0.1 per cent sulphuric acid and 0.25 per cent sodium sulphate, and the bath liquor fails to give a positive response to the so-called biuret test for protein degradation products.

The fibre is then immersed in 20 times its weight of 40 per cent formalin at room temperature to 3 which has been added suflicient sulphuric acid to give the solution a pH of 3.3 as measured on an electrometric pH meter and is allowed to remain for 40 minutes in the solution. The staple fibre is thenremoved and is thoroughly washed with water, soaked in an 0.06 per cent solution of sodium cetyl sulphate and then in 0.5 per cent sodium carbonate solution, and again thoroughly washed in water and dried at 100 C. When measured on the Cliff Autographic Recorder its strength is now approximately 11 kilograms per square millimetre. For the tensile strength measurements the staple fibre is brought into equilibrium with an atmosphere of 60 per cent relative humidity.

We claim:

1. The method for the production of protein filaments which comprises insolubilizing coag- V ulated protein filaments by treatment with an acidic, saline solution of formaldehyde and, thereafter, contacting the insolubilized filaments for a time corresponding to about 30 to 45 minutes at room temperature with a formaldehyde solution of approximately 40% formaldehyde concentration having a pH between about 1.9 and 4.0. 2. The method of claim 1 wherein said pH is between 2.0 and 3.5.

3. The method of claim 1 wherein said insolubilized filaments are contacted with the formaldehyde treating solution by immersion in said solution in a relaxed condition.

[4. The method for the production of protein filaments which comprises insolubilizing coagulated protein filaments by treatment with an acidic saline solution of formaldehyde, washing the insolubilized filaments in order to free them from adhering acid and salts and, thereafter, contacting the insolubilized filaments for a time corresponding to about 30 to 45 minutes at room 4 temperature with a formaldehyde solution of approximately 40% formaldehyde concentration having a pI-I between about 1.9 and 4.0.

5. The method of claim 1 wherein the protein filaments are coagulated peanut globulin filaments.'

6. Artificial protein filaments prepared in accordance with the process of claim 1.

7. The method of claim 1, wherein the proportion of the acidic formaldehyde treatment solution to the proportion of filament being treated is about 20 to 1 by weight.

ROBIN H. K. THOMSON. DAVID TRAILL.

' REFERENCES CITED The following references are of record in the file of this patent:

OTHER REFERENCES Kats et al., J. Applied Chem. (USSR), 1943, 16, 134-142, Abst. in J. Text. Inst, July 1944, page A283. 

1. THE METHOD FOR THE PRODUCTION OF PROTEIN FILAMENTS WHICH COMPRISES INSOLUBILIZING COAGULATED PROTEIN FILAMENTS BY TREATMENT WITH AN ACIDIC, SALINE SOLUTION OF FORMALEHYDE AND, THEREAFTER, CONTACTING THE INSOLUBILIZED FILAMENTS FOR A TIME CORRESPONDING TO ABOUT 30 TO 45 MINUTES AT ROOM TEMPERATURE WITH A FORMALDEHYDE SOLUTION OF APPROXIMATELY 40% FORMALDEHYDE CONCENTRATION HAVING A PH BETWEEN ABOUT 1.9 AND 4.0. 